The receptor for advanced glycation end products (RAGE) is a cellular binding site for amphoterin. Mediation of neurite outgrowth and co-expression of rage and amphoterin in the developing nervous system

Anti-inflammatory antioxidants attenuate the expression of inducible nitric oxide synthase mediated by advanced glycation endproducts in murine microglia

Advanced glycation endproducts (AGEs) accumulate on long-lived protein deposits including beta-amyloid plaques in Alzheimer's disease (AD). AGE-modified amyloid deposits contain oxidized and nitrated proteins as markers of a chronic neuroinflammatory condition and are surrounded by activated microglial and astroglial cells. We show in this study that AGEs increase nitric oxide production by induction of the inducible nitric oxide synthase (iNOS) on the mRNA and protein level in the murine microglial cell line N-11. Membrane permeable antioxidants including oestrogen derivatives (e.g. 17beta-oestradiol) thiol antioxidants (e.g. (R+)-alpha-lipoic acid) and Gingko biloba extract EGb 761, but not phosphodiesterase inhibitors such as propentophylline, prevent the up-regulation of AGE-induced iNOS expression and NO production. These results indicate that oxygen free radicals serve as second messengers in AGE-induced pro-inflammatory signal transduction pathways. As this pharmacological mechanism is not only relevant for Alzheimer's disease, but also for many chronic inflammatory conditions, such membrane-permeable antioxidants could be regarded not only as antioxidant, but also as potent therapeutic anti-inflammatory drugs.

RAGE expression and AGE-induced MAP kinase activation in Caco-2 cells

RAGE (receptor for advanced glycation end products) is a multiligand cell surface molecule of the immunoglobulin superfamily. It was originally described as a receptor for protein adducts formed by glycoxidation (AGEs) that accumulate in diseases such as diabetes and renal failure. Performing RT-PCR and Western blot analysis we intended to determine RAGE expression in the human colon adenocarcinoma cell line Caco-2. Moreover, Caco-2 cells were incubated in the presence of AGEs. Since RAGE ligation triggers the p21(ras) signal transduction pathway the activation state of p44/42 (ERK1/2) MAP kinases was determined. Here we demonstrate for the first time that Caco-2 cells express RAGE and that administration of the food-derived casein-linked AGE N(epsilon)-(carboxymethyl)lysine (Cas-CML) results in Caco-2 p44/42 (ERK1/2) MAP kinase activation.

S100A12 protein is a strong inducer of neurite outgrowth from primary hippocampal neurons

Several members of the S100 family of Ca(2+) binding proteins are at present known to be secreted and to have extracellular activities. We have investigated the neurite inducing potential of extracellularly added S100A12. Human recombinant S100A12 was found to dramatically induce neuritogenesis of hippocampal cells isolated from 17 to 19 days old rat embryos. The response to S100A12 was dependent on the dose in a bell-shaped manner. A 10-fold increase in neurite outgrowth was observed upon treatment with S100A12 in concentrations between 0.1 and 2.0 microM already after 24 h. Exposure to S100A12 for only 15 min was enough to induce neuritogenesis when measured after 24 h, but to obtain a maximal response, S100A12 had to be present in the culture for at least 4 h. The response to S100A12 was abolished by inhibitors of phospholipase C (PLC), protein kinase C (PKC), Ca(2+) flux, Ca(2+)/calmodulin dependent kinase II (CaMKII) or mitogen-activated protein kinase kinase (MEK). Therefore, we suggest that extracellular S100A12 triggers intracellular signal transduction in neurons, involving the classical mitogen-activated protein (MAP) kinase pathway and a phospholipase C-generated second messenger pathway leading to an increase in intracellular Ca(2+) and activation of PKC, ultimately resulting in neuronal differentiation.

Familial amyloid polyneuropathy: receptor for advanced glycation end products-dependent triggering of neuronal inflammatory and apoptotic pathways

Familial amyloid polyneuropathy (FAP) is a neurodegenerative disorder associated with extracellular deposition of mutant transthyretin (TTR) amyloid fibrils, particularly in the peripheral nervous system. We have hypothesized that binding of TTR fibrils to the receptor for advanced glycation end products (RAGE) on critical cellular targets is associated with a destructive stress response underlying peripheral nerve dysfunction. Analysis of nerve biopsy samples from patients with FAP (n = 16) at different stages of disease (0-3), compared with age-matched controls (n = 4), by semiquantitative immunohistology and in situ hybridization showed increased levels of RAGE, beginning at the earliest stages of the disease (FAP 0; p < 0.02) and especially localized in axons. Upregulation of proinflammatory cytokines (tumor necrosis factor-alpha and interleukin-1beta) (approximately threefold; p < 0.02) and the inducible form of nitric oxide synthase (iNOS) ( approximately 2.5-fold; p < 0.04) was also observed in a distribution overlapping RAGE expression. Tyrosine nitration and increased activated caspase-3 in axons from FAP patients (p < 0.03) were apparent. Although these data suggest the presence of ongoing neuronal stress, there was no upregulation of neurotrophins (nerve growth factor and neurotrophin-3) in FAP nerves. Studies on cultured neuronal-like, Schwann, and endothelial cells incubated with TTR fibrils displayed RAGE-dependent expression of cytokines and iNOS at early times (6 and 12 hr, respectively), followed by later (24 hr) activation of caspase-3 and DNA fragmentation. We propose that the interaction of TTR fibrils with RAGE may contribute to cellular stress and toxicity in FAP. Furthermore, there is an apparent lack of responsiveness of Schwann cells in FAP nerve to provide neurotrophic factors.

Involvement of microglial receptor for advanced glycation endproducts (RAGE) in Alzheimer's disease: identification of a cellular activation mechanism

Receptor-mediated interactions with amyloid beta-peptide (Abeta) could be important in the evolution of the inflammatory processes and cellular dysfunction that are prominent in Alzheimer's disease (AD) pathology. One candidate receptor is the receptor for advanced glycation endproducts (RAGE), which can bind Abeta and transduce signals leading to cellular activation. Data are presented showing a potential mechanism for Abeta activation of microglia that could be mediated by RAGE and macrophage colony-stimulating factor (M-CSF). Using brain tissue from AD and nondemented (ND) individuals, RAGE expression was shown to be present on microglia and neurons of the hippocampus, entorhinal cortex, and superior frontal gyrus. The presence of increased numbers of RAGE-immunoreactive microglia in AD led us to further analyze RAGE-related properties of these cells cultured from AD and ND brains. Direct addition of Abeta(1-42) to the microglia increased their expression of M-CSF. This effect was significantly greater in microglia derived from AD brains compared to those from ND brains. Increased M-CSF secretion was also demonstrated using a cell culture model of plaques whereby microglia were cultured in wells containing focal deposits of immobilized Abeta(1-42). In each case, the Abeta stimulation of M-CSF secretion was significantly blocked by treatment of cultures with anti-RAGE F(ab')2. Treatment of microglia with anti-RAGE F(ab')2 also inhibited the chemotactic response of microglia toward Abeta(1-42). Finally, incubation of microglia with M-CSF and Abeta increased expression of RAGE mRNA. These microglia also expressed M-CSF receptor mRNA. These data suggest a positive feedback loop in which Abeta-RAGE-mediated microglial activation enhances expression of M-CSF and RAGE, possibly initiating an ascending spiral of cellular activation.

Borna disease virus phosphoprotein binds a neurite outgrowth factor, amphoterin/HMG-1

The Borna disease virus (BDV) p24 phosphoprotein is an abundant protein in BDV-infected cultured cells and animal brains. Therefore, there is a possibility that binding of the p24 protein to cellular factor(s) induces functional alterations of infected neural cells in the brain. To identify a cellular protein(s) that interacts with BDV p24 protein, we performed far-Western blotting with extracts from various cell lines. Using recombinant p24 protein as a probe, we detected a 30-kDa protein in all cell lines examined. Binding between the 30-kDa and BDV p24 proteins was also demonstrated using BDV p24 affinity and ion-exchange chromatography columns. Microsequence analysis of the purified 30-kDa protein revealed that its N terminus showed complete homology with rat amphoterin protein, which is a neurite outgrowth factor abundant in the brain during development. Mammalian two-hybrid and immunoprecipitation analyses also confirmed that amphoterin is a specific target for the p24 protein in vivo. Furthermore, we showed that infection by BDV, as well as purified p24 protein in the medium, significantly decreased cell process outgrowth of cells grown on laminin, indicating the functional inhibition of amphoterin by interaction with the p24 protein. Immunohistochemical analysis revealed decreased levels of amphoterin protein at the leading edges of BDV-infected cells. Moreover, the expression of the receptor for advanced glycation end products, of which the extracellular moiety is a receptor for amphoterin, was not significantly activated in BDV-infected cells during the process of extension, suggesting that the secretion of amphoterin from the cell surface is inhibited by the binding of the p24 protein. These results suggested that BDV infection may cause direct damage in the developing brain by inhibiting the function of amphoterin due to binding by the p24 phosphoprotein.

Amphoterin includes a sequence motif which is homologous to the Alzheimer's beta-amyloid peptide (Abeta), forms amyloid fibrils in vitro, and binds avidly to Abeta

Many of the proteins associated with amyloidoses have been found to share structural and sequence similarities, which are believed to be responsible for their capability to form amyloid fibrils. Interestingly, some proteins seem to be able to form amyloid-like fibrils although they are not associated with amyloidoses. This indicates that the ability to form amyloid fibrils may be a general property of a greater number of proteins not associated with these diseases. In the present work, we have searched for amyloidogenic consensus sequences in two current protein/peptide databases and show that many proteins share structures which can be predicted to form amyloid. One of these potentially amyloidogenic proteins is amphoterin (also known as HMG-1), involved in neuronal development and a ligand for the receptor for advanced glycation end products (RAGE). It contains an amyloidogenic peptide fragment which is highly homologous to the Alzheimer's amyloid beta-peptide. If enzymatically released from the native protein, it forms amyloid-like fibrils which are visible in electron microscopy, exhibit apple green birefringence under polarized light after Congo red staining, and increases thioflavin T fluorescence. This fragment also shows high affinity to Abeta as a free peptide or while part of the native protein. Our results support the hypothesis that the potential to form amyloid is a common characteristic of a number of proteins, independent of their relation to amyloidoses, and that this potential can be predicted based on the physicochemical properties of these proteins.

Development and prevention of advanced diabetic nephropathy in RAGE-overexpressing mice

Vascular complications arising from multiple environmental and genetic factors are responsible for many of the disabilities and short life expectancy associated with diabetes mellitus. Here we provide the first direct in vivo evidence that interactions between advanced glycation end products (AGEs; nonenzymatically glycosylated protein derivatives formed during prolonged hyperglycemic exposure) and their receptor, RAGE, lead to diabetic vascular derangement. We created transgenic mice that overexpress human RAGE in vascular cells and crossbred them with another transgenic line that develops insulin-dependent diabetes shortly after birth. The resultant double transgenic mice exhibited increased hemoglobin A(1c) and serum AGE levels, as did the diabetic controls. The double transgenic mice demonstrated enlargement of the kidney, glomerular hypertrophy, increased albuminuria, mesangial expansion, advanced glomerulosclerosis, and increased serum creatinine compared with diabetic littermates lacking the RAGE transgene. To our knowledge, the development of this double transgenic mouse provides the first animal model that exhibits the renal changes seen in humans. Furthermore, the phenotypes of advanced diabetic nephropathy were prevented by administering an AGE inhibitor, (+/-)-2-isopropylidenehydrazono-4-oxo-thiazolidin-5-ylacetanilide (OPB-9195), thus establishing the AGE-RAGE system as a promising target for overcoming this aspect of diabetic pathogenesis.

Extracellular processing of amphoterin generates a peptide active on erythroleukaemia cell differentiation

The release of amphoterin by murine erythroleukaemia cells exposed to the chemical inducer hexamethylenebisacetamide represents an essential step for the process of their terminal differentiation. Once exported in the culture medium, amphoterin undergoes limited proteolysis, catalysed by a serine proteinase also secreted by stimulated cells. The isolated proteinase is responsible for degradation of amphoterin, with the production of a 10-amino-acid-residue fragment, specifically retaining the cell-differentiation-stimulating activity of the native protein molecule. This peptide does not express other properties of amphoterin, such as protein kinase C-stimulating activity or systemic toxicity. These findings define a selective mechanism accounting for extracellular amphoterin functional maturation.

S100: a multigenic family of calcium-modulated proteins of the EF-hand type with intracellular and extracellular functional roles

S100 is a multigenic family of non-ubiquitous Ca(2+)-modulated proteins of the EF-hand type expressed in vertebrates exclusively and implicated in intracellular and extracellular regulatory activities. Within cells, most of S100 members exist in the form of antiparallelly packed homodimers (in some cases heterodimers), capable of functionally crossbridging two homologous or heterologous target proteins in a Ca(2+)-dependent (and, in some instances, Ca(2+)-independent) manner. S100 oligomers can also form, under the non-reducing conditions found in the extracellular space and/or within cells upon changes in the cell redox status. Within cells, S100 proteins have been implicated in the regulation of protein phosphorylation, some enzyme activities, the dynamics of cytoskeleton components, transcription factors, Ca(2+) homeostasis, and cell proliferation and differentiation. Certain S100 members are released into the extracellular space by an unknown mechanism. Extracellular S100 proteins stimulate neuronal survival and/or differentiation and astrocyte proliferation, cause neuronal death via apoptosis, and stimulate (in some cases) or inhibit (in other cases) the activity of inflammatory cells. A cell surface receptor, RAGE, has been identified on inflammatory cells and neurons for S100A12 and S100B, which transduces S100A12 and S100B effects. It is not known whether RAGE is a universal S100 receptor, S100 members interact with other cell surface receptors, or S100 protein interaction with other extracellular factors specifies the biological effects of a given S100 protein on a target cell. The variety of intracellular target proteins of S100 proteins and, in some cases, of a single S100 protein, and the cell specificity of expression of certain S100 members suggest that these proteins might have a role in the fine regulation of effector proteins and/or specific steps of signaling pathways/cellular functions. Future analyses should discriminate between functionally relevant S100 interactions with target proteins and in vitro observations devoid of physiological importance.

Activation of NADPH oxidase by AGE links oxidant stress to altered gene expression via RAGE

Engagement of the receptor for advanced glycation end products (RAGE) by products of nonenzymatic glycation/oxidation triggers the generation of reactive oxygen species (ROS), thereby altering gene expression. Because dissection of the precise events by which ROS are generated via RAGE is relevant to the pathogenesis of complications in AGE-related disorders, such as diabetes and renal failure, we tested the hypothesis that activation of NADPH oxidase contributed, at least in part, to enhancing oxidant stress via RAGE. Here we show that incubation of human endothelial cells with AGEs on the surface of diabetic red blood cells, or specific AGEs, (carboxymethyl)lysine (CML)-modified adducts, prompted intracellular generation of hydrogen peroxide, cell surface expression of vascular cell adhesion molecule-1, and generation of tissue factor in a manner suppressed by treatment with diphenyliodonium, but not by inhibitors of nitric oxide. Consistent with an important role for NADPH oxidase, although macrophages derived from wild-type mice expressed enhanced levels of tissue factor upon stimulation with AGE, macrophages derived from mice deficient in a central subunit of NADPH oxidase, gp91phox, failed to display enhanced tissue factor in the presence of AGE. These findings underscore a central role of NADPH oxidase in AGE-RAGE-mediated generation of ROS and provide a mechanism for altered gene expression in AGE-related disorders.

A novel polymorphism in the promoter of the RAGE gene is associated with non-small cell lung cancer

The receptor for advanced glycosylation endproducts (RAGE) is abundant at both the transcriptional and translational level in normal lung but is not expressed in non-small cell lung cancer (NSCLC). In order to determine whether sequence variations might be responsible for the inactivation of RAGE in NSCLC, we investigated the RAGE gene in primary NSCLCs and in the corresponding normal tissues of nine patients. Although sequence analysis revealed no somatic, tumor-associated mutations, six novel sequence variants were identified: T-->A in the promoter region 388 bp upstream of the start codon: T-->A in exon 1 (Ala2Ala), C-->G in exon 3 (Val89Val), C-->T in intron 6, G-->C and C-->G in exon 10 (Arg365Ser and Arg369Gly). In addition, we detected a 63 bp deletion in the promoter region (358-421 bp upstream of the start codon) in one NSCLC patient. The T-->A transversion in the promoter region was detected in three of nine patients. Further analysis of this polymorphic locus in 54 NSCLC patients and 59 non-cancer controls revealed a significant difference in the genotype distribution between NSCLC patients and controls. Interestingly, the AA genotype was more common in NSCLC patients (20.8%) than in controls (3.5%). The cumulative occurrence of the AA variant in NSCLC suggests that this genotype is a putative risk factor for NSCLC development.

The high mobility group (HMG) boxes of the nuclear protein HMG1 induce chemotaxis and cytoskeleton reorganization in rat smooth muscle cells

HMG1 (high mobility group 1) is a ubiquitous and abundant chromatin component. However, HMG1 can be secreted by activated macrophages and monocytes, and can act as a mediator of inflammation and endotoxic lethality. Here we document a role of extracellular HMG1 in cell migration. HMG1 (and its individual DNA-binding domains) stimulated migration of rat smooth muscle cells in chemotaxis, chemokinesis, and wound healing assays. HMG1 induced rapid and transient changes of cell shape, and actin cytoskeleton reorganization leading to an elongated polarized morphology typical of motile cells. These effects were inhibited by antibodies directed against the receptor of advanced glycation endproducts, indicating that the receptor of advanced glycation endproducts is the receptor mediating the HMG1-dependent migratory responses. Pertussis toxin and the mitogen-activated protein kinase kinase inhibitor PD98059 also blocked HMG1-induced rat smooth muscle cell migration, suggesting that a G(i/o) protein and mitogen-activated protein kinases are required for the HMG1 signaling pathway. We also show that HMG1 can be released by damage or necrosis of a variety of cell types, including endothelial cells. Thus, HMG1 has all the hallmarks of a molecule that can promote atherosclerosis and restenosis after vascular damage.

Coregulation of neurite outgrowth and cell survival by amphoterin and S100 proteins through receptor for advanced glycation end products (RAGE) activation

Amphoterin is a protein enhancing process extension and migration in embryonic neurons and in tumor cells through binding to receptor for advanced glycation end products (RAGE), a multiligand transmembrane receptor. S100 proteins, especially S100B, are abundantly expressed in the nervous system and are suggested to function as cytokines with both neurotrophic and neurotoxic effects. However, the cell surface receptor for the cytokine function of S100B has not been identified. Here we show that two S100 family proteins, S100B and S100A1, activate RAGE in concert with amphoterin inducing neurite outgrowth and activation of transcription factor NF-kappaB. Furthermore, activation of RAGE by amphoterin and S100B promotes cell survival through increased expression of the anti-apoptotic protein Bcl-2. However, whereas nanomolar concentrations of S100B induce trophic effects in RAGE-expressing cells, micromolar concentrations of S100B induce apoptosis in an oxidant-dependent manner. Both trophic and toxic effects are specific for cells expressing full-length RAGE since cells expressing a cytoplasmic domain deletion mutant of RAGE are unresponsive to these stimuli. These findings suggest that activation of RAGE by multiple ligands is able to promote trophic effects whereas hyperactivation of RAGE signaling pathways promotes apoptosis. We suggest that RAGE is a signal-transducing receptor for both trophic and toxic effects of S100B.

The biology of the receptor for advanced glycation end products and its ligands

Receptor for advanced glycation end products (RAGE) is a multiligand member of the immunoglobulin superfamily of cell surface molecules whose repertoire of ligands includes advanced glycation end products (AGEs), amyloid fibrils, amphoterins and S100/calgranulins. The overlapping distribution of these ligands and cells overexpressing RAGE results in sustained receptor expression which is magnified via the apparent capacity of ligands to upregulate the receptor. We hypothesize that RAGE-ligand interaction is a propagation factor in a range of chronic disorders, based on the enhanced accumulation of the ligands in diseased tissues. For example, increased levels of AGEs in diabetes and renal insufficiency, amyloid fibrils in Alzheimer's disease brain, amphoterin in tumors and S100/calgranulins at sites of inflammation have been identified. The engagement of RAGE by its ligands can be considered the 'first hit' in a two-stage model, in which the second phase of cellular perturbation is mediated by superimposed accumulation of modified lipoproteins (in atherosclerosis), invading bacterial pathogens, ischemic stress and other factors. Taken together, these 'two hits' eventuate in a cellular response with a propensity towards tissue destruction rather than resolution of the offending pathogenic stimulus. Experimental data are cited regarding this hypothesis, though further studies will be required, especially with selective low molecular weight inhibitors of RAGE and RAGE knockout mice, to obtain additional proof in support of our concept.

HMG-1 as a mediator of acute lung inflammation

Acute inflammatory lung injury is often a delayed complication of critical illness and is associated with increased mortality. High mobility group-1 (HMG-1) protein, in addition to its role as a transcriptional regulatory factor, has recently been identified as a late mediator of endotoxin lethality. In the present studies, HMG-1 given intratracheally produced acute inflammatory injury to the lungs, with neutrophil accumulation, the development of lung edema, and increased pulmonary production of IL-1beta, TNF-alpha, and macrophage-inflammatory protein-2. In endotoxin-induced acute lung inflammation, administration of anti-HMG-1 Abs either before or after endotoxin exposure decreased the migration of neutrophils to the lungs as well as lung edema. These protective effects of anti-HMG-1 were specific, because pulmonary levels of IL-1beta, TNF-alpha, or macrophage-inflammatory protein-2 were not decreased after therapy with anti-HMG-1. Together, these findings indicate that HMG-1 is a distal mediator of acute inflammatory lung injury.

Heparin-binding proteins HB-GAM (pleiotrophin) and amphoterin in the regulation of cell motility

Fractionation of proteins from perinatal rat brain was monitored using a neurite outgrowth assay. Two neurite-promoting proteins, HB-GAM (heparin-binding growth-associated molecule; also known as pleiotrophin) and amphoterin, were isolated, cloned and produced by baculovirus expression for structural and functional studies. HB-GAM is highly expressed in embryonic and early post-natal fiber pathways of the nervous system, and it enhances axonal growth/guidance by binding to N-syndecan (syndecan-3) at the neuron surface. N-syndecan in turn communicates with the cytoskeleton through the cortactin/src-kinase pathway to enhance neurite extension. In addition to N-syndecan, the chondroitin sulfate proteoglycan RPTP beta/zeta (receptor-type tyrosine phosphatase beta/zeta) is implicated in the receptor mechanism of HB-GAM. HB-GAM is also prominently expressed in developing and regenerating bone as a matrix-bound cue for migration of osteoblasts/osteoblast precursors to the site of bone deposition. HB-GAM is suggested to regulate motility in osteoblasts through a similar mechanism as in neurons. Structural studies using heteronuclear NMR reveal two similar protein domains in HB-GAM, both consisting of three anti-parallel beta-strands. Search of sequence databases shows that the beta structures of HB-GAM and of the similar domains of MK (midkine) correspond to the thrombospondin type I (TSR) sequence motif. We suggest that the TSR sequence motif, found in several neurite outgrowth-promoting and other cell surface and matrix-binding proteins, defines a beta structure similar to those found in HB-GAM and MK. In general, amphoterin is highly expressed in immature and transformed cells. We suggest a model, according to which amphoterin is an autocrine/paracrine regulator of invasive migration. Amphoterin binds to RAGE (receptor of advanced glycation end products), an immunoglubulin superfamily member related to N-CAM (neural cell adhesion molecule), that communicates with the GTPases Cdc42 and Rac to regulate cell motility. In addition, ligation of RAGE by amphoterin activates NF-kappaB to regulate transcription.

Expression of advanced glycation end products and their cellular receptor RAGE in diabetic nephropathy and nondiabetic renal disease

Advanced glycation end products (AGE) contribute to diabetic tissue injury by two major mechanisms, i.e., the alteration of extracellular matrix architecture through nonenzymatic glycation, with formation of protein crosslinks, and the modulation of cellular functions through interactions with specific cell surface receptors, the best characterized of which is the receptor for AGE (RAGE). Recent evidence suggests that the AGE-RAGE interaction may also be promoted by inflammatory processes and oxidative cellular injury. To characterize the distributions of AGE and RAGE in diabetic kidneys and to determine their specificity for diabetic nephropathy, an immunohistochemical analysis of renal biopsies from patients with diabetic nephropathy (n = 26), hypertensive nephrosclerosis (n = 7), idiopathic focal segmental glomerulosclerosis (n = 11), focal sclerosis secondary to obesity (n = 7), and lupus nephritis (n = 11) and from normal control subjects (n = 2) was performed, using affinity-purified antibodies raised to RAGE and two subclasses of AGE, i.e., N(epsilon)-(carboxymethyl)-lysine (CML) and pentosidine (PENT). AGE were detected equally in diffuse and nodular diabetic nephropathy. CML was the major AGE detected in diabetic mesangium (96%), glomerular basement membranes (GBM) (42%), tubular basement membranes (85%), and vessel walls (96%). In diabetic nephropathy, PENT was preferentially located in interstitial collagen (90%) and was less consistently observed in vessel walls (54%), mesangium (77%), GBM (4%), and tubular basement membranes (31%). RAGE was expressed on normal podocytes and was upregulated in diabetic nephropathy. The restriction of RAGE mRNA expression to glomeruli was confirmed by reverse transcription-PCR analysis of microdissected renal tissue compartments. The extent of mesangial and GBM immunoreactivity for CML, but not PENT, was correlated with the severity of diabetic glomerulosclerosis, as assessed pathologically. CML and PENT were also identified in areas of glomerulosclerosis and arteriosclerosis in idiopathic and secondary focal segmental glomerulosclerosis, hypertensive nephrosclerosis, and lupus nephritis. In active lupus nephritis, CML and PENT were detected in the proliferative glomerular tufts and crescents. In conclusion, CML is a major AGE in renal basement membranes in diabetic nephropathy, and its accumulation involves upregulation of RAGE on podocytes. AGE are also accumulated in acute inflammatory glomerulonephritis secondary to systemic lupus erythematosus, possibly via enzymatic oxidation of glomerular matrix proteins.

The receptor for advanced glycation end products is induced by the glycation products themselves and tumor necrosis factor-alpha through nuclear factor-kappa B, and by 17beta-estradiol through Sp-1 in human vascular endothelial cells

The binding of advanced glycation end products (AGE) to the receptor for AGE (RAGE) is known to deteriorate various cell functions and is implicated in the pathogenesis of diabetic vascular complications. Here we show that AGE, tumor necrosis factor-alpha (TNF-alpha), and 17beta-estradiol (E(2)) up-regulated RAGE mRNA and protein levels in human microvascular endothelial cells and ECV304 cells, with the mRNA stability being essentially invariant. Transient transfection experiments with human RAGE promoter-luciferase chimeras revealed that the region from nucleotide number -751 to -629 and the region from -239 to -89 in the RAGE 5'-flanking sequence exhibited the AGE/TNF-alpha and E(2) responsiveness, respectively. Site-directed mutation of an nuclear factor-kappaB (NF-kappaB) site at -671 or of Sp-1 sites at -189 and -172 residing in those regions resulted in an abrogation of the AGE/TNF-alpha- or E(2)-mediated transcriptional activation. Electrophoretic mobility shift assays revealed that ECV304 cell nuclear extracts contained factors which retarded the NF-kappaB and Sp-1 elements, and that the DNA-protein complexes were supershifted by anti-p65/p50 NF-kappaB and anti-Sp-1/estrogen receptor alpha antibodies, respectively. These results suggest that AGE, TNF-alpha, and E(2) can activate the RAGE gene through NF-kappaB and Sp-1, causing enhanced AGE-RAGE interactions, which would lead to an exacerbation of diabetic microvasculopathy.

Cellular cofactors potentiating induction of stress and cytotoxicity by amyloid beta-peptide

Insights into factors underlying causes of familial Alzheimer's disease (AD), such as mutant forms of beta-amyloid precursor protein and presenilins, and those conferring increased risk of sporadic AD, such as isoforms of apolipoprotein E and polymorphisms of alpha2-macroglobulin, have been rapidly emerging. However, mechanisms through which amyloid beta-peptide (Abeta), the fibrillogenic peptide most closely associated with neurotoxicity in AD, exerts its effects on cellular targets have only been more generally outlined. Late in the course of AD, when Abeta fibrils are abundant, non-specific interactions of amyloid with cellular elements are likely to induce broad cytotoxicity. However, early in AD, when concentrations of Abeta are much lower and extracellular deposits are infrequent, mechanisms underlying cellular dysfunction have not been clearly defined. The key issue in elucidating the means through which Abeta perturbs cellular properties early in AD is the possibility that protective therapy at such times may prevent cytotoxicity at a point when damage is still reversible. This brief review focusses on two cellular cofactors for Abeta-induced cellular perturbation: the cell surface immunoglobulin superfamily molecule RAGE (receptor for advanced glycation endproducts) and ABAD (Abeta binding alcohol dehydrogenase). Although final proof for the involvement of these cofactors in cellular dysfunction in AD must await the results of further in vivo experiments, their increased expression in AD brain, as well as other evidence described below, suggests the possibility of specific pathways for Abeta-induced cellular perturbation which could provide future therapeutic targets.

Interaction of the receptor for advanced glycation end products (RAGE) with transthyretin triggers nuclear transcription factor kB (NF-kB) activation

Mutated transthyretin (TTR) fibrils are associated with the pathology of familial amyloidotic polyneuropathy (FAP), in which extracellular amyloid deposits lead to degeneration of cells and tissues, in particular neurons of the peripheral nerve. Here we present evidence that the receptor for advanced glycation end products (RAGE), previously associated with Alzheimer's disease, acts as a selective cell surface acceptor site for both soluble and fibrillar TTR. Immunohistochemical studies demonstrating increased expression of RAGE in FAP tissues suggested the relevance of this receptor to TTR-induced fibrillar pathology. In vitro studies using soluble RAGE showed saturable specific interaction with soluble and fibrillar TTR with a K(d) of approximately 120 nM. However, no binding was observed when soluble TTR was combined with retinol-binding protein, which represents the form in which TTR normally circulates in plasma. Specific binding of TTR to RAGE-transfected Chinese hamster ovary cells (which was completely blocked by anti-RAGE) was observed, confirming that RAGE could mediate TTR binding to cellular surfaces. RAGE-dependent activation of nuclear transcription factor kB (NF-kB) by TTR fibrils was shown in PC-12 cells stably transfected to overexpress the receptor. Furthermore, FAP nerves showed up-regulation of p50, one of the NF-kB subunits, when compared with age-matched controls. From these observations we predict that, in vivo, the presence of TTR fibrils associated with cellular surfaces of FAP patients, by contributing to NF-kB activation, leads to the pathogenesis of neurodegeneration. Further insights into the consequences of the interaction of fibrillar TTR with RAGE may therefore provide a better understanding of neurodegeneration associated with FAP.

Receptor-dependent cell stress and amyloid accumulation in systemic amyloidosis

Accumulation of fibrils composed of amyloid A in tissues resulting in displacement of normal structures and cellular dysfunction is the characteristic feature of systemic amyloidoses. Here we show that RAGE, a multiligand immunoglobulin superfamily cell surface molecule, is a receptor for the amyloidogenic form of serum amyloid A. Interactions between RAGE and amyloid A induced cellular perturbation. In a mouse model, amyloid A accumulation, evidence of cell stress and expression of RAGE were closely linked. Antagonizing RAGE suppressed cell stress and amyloid deposition in mouse spleens. These data indicate that RAGE is a potential target for inhibiting accumulation of amyloid A and for limiting cellular dysfunction induced by amyloid A.

Blockade of RAGE-amphoterin signalling suppresses tumour growth and metastases

The receptor for advanced glycation end products (RAGE), a multi-ligand member of the immunoglobulin superfamily of cell surface molecules, interacts with distinct molecules implicated in homeostasis, development and inflammation, and certain diseases such as diabetes and Alzheimer's disease. Engagement of RAGE by a ligand triggers activation of key cell signalling pathways, such as p21ras, MAP kinases, NF-kappaB and cdc42/rac, thereby reprogramming cellular properties. RAGE is a central cell surface receptor for amphoterin, a polypeptide linked to outgrowth of cultured cortical neurons derived from developing brain. Indeed, the co-localization of RAGE and amphoterin at the leading edge of advancing neurites indicated their potential contribution to cellular migration, and in pathologies such as tumour invasion. Here we demonstrate that blockade of RAGE-amphoterin decreased growth and metastases of both implanted tumours and tumours developing spontaneously in susceptible mice. Inhibition of the RAGE-amphoterin interaction suppressed activation of p44/p42, p38 and SAP/JNK MAP kinases; molecular effector mechanisms importantly linked to tumour proliferation, invasion and expression of matrix metalloproteinases.

Regulation of cell migration by amphoterin

Amphoterin, a major form of HMG (high mobility group) 1 proteins, is highly expressed in immature and malignant cells. A role in cell motility is suggested by the ability of amphoterin to promote neurite extension through RAGE (receptor of advanced glycation end products), an immunoglobulin superfamily member that communicates with the GTPases Cdc42 and Rac. We show here that cell contact with the laminin matrix induces accumulation of both amphoterin mRNA and protein close to the plasma membrane, which is accompanied by extracellular export of amphoterin. A role for amphoterin in extracellular matrix-dependent cell regulation is further suggested by the finding that specific decrease of amphoterin mRNA and protein, using antisense oligonucleotides transfected into cells, inhibits cell migration to laminin in a transfilter assay whereas the oligonucleotides in the culture medium have no effect. Moreover, affinity-purified anti-amphoterin antibodies inhibit cell migration to laminin, supporting an extracellular role for the endogenous amphoterin in cell motility. The finding that amphoterin expression is more pronounced in cells with a motile phenotype as compared to cells of dense cultures, is consistent with the results of the cell migration assays. Our results strongly suggest that amphoterin is a key player in the migration of immature and transformed cells.

Differential expression of S100B and S100A6(1) in the human fetal and aged cerebral cortex

S100B and S100A6 (calcylin) are two members of the S100 Ca(2+)-binding protein family and have been localized in the mammalian nervous system. However, information on their distribution in the human nervous system, especially in the developing human fetal brain, is scarce. In the present study, an immunocytochemical method was used to examine the spatio-temporal protein expression patterns of S100B and S100A6 in normal human fetal hippocampus, entorhinal cortex and occipital cortex. Normal aged adult human brain specimens were also included for comparison. From week 15 onwards, an increase with advancing gestation age in both the number and staining intensity of S100B positive, astrocyte-like cells was found in the pyramidal layer of the hippocampus, while both the molecular and polymorphic layers showed similar S100B immunoreactivities at all stages examined. A decrease in the immunoreactivities was found in the molecular layer of the aged adult hippocampus while other layers exhibited immunoreactivities similar to those of the late fetus. At week 15, the molecular, pyramidal and ganglionic/multiform layers of the entorhinal cortex also showed positive S100B immunoreactivities which were maintained throughout the rest of the gestation and in adult specimens. In the occipital cortex, the numbers of positive cells for all layers were about twofold higher than those found in the hippocampus and entorhinal cortex, and immunoreactivities detected in the granular layer increased from week 21, reaching a plateau at around week 27. S100B positive fibers were also found at week 30 but were not observed in aged adult specimens. S100A6 positive cells were on the whole fewer in number than those of S100B in the brain regions examined. The S100A6 immunoreactivities which were localized in some pyramidal neuron-like and some glial-like cells of the pyramidal and molecular layers of the hippocampus increased by midgestation and became weak in the late fetus and in aged adult specimens. Weakly stained S100A6 positive cells were also observed in the entorhinal cortex throughout the gestation and in aged adult cortex. S100A6 immunoreactivities were weak in the fetal occipital cortex. They were also localized in the glial-like cells of the aged adult occipital cortex. The differential spatio-temporal expression of S100B and S100A6 proteins suggests that the proteins play different roles in different brain regions during development and in adulthood.

The chondroitin sulfate proteoglycans neurocan and phosphacan are expressed by reactive astrocytes in the chronic CNS glial scar

Chondroitin sulfate proteoglycans (CS-PGs) expressed by reactive astrocytes may contribute to the axon growth-inhibitory environment of the injured CNS. The specific potentially inhibitory CS-PGs present in areas of reactive gliosis, however, have yet to be thoroughly examined. In this study, we used immunohistochemistry, combined immunohistochemistry-in situ hybridization, immunoblot analysis, and reverse transcription-PCR to examine the expression of specific CS-PGs by reactive astrocytes in an in vivo model of reactive gliosis: that is, the glial scar, after cortical injury. Neurocan and phosphacan can be localized to reactive astrocytes 30 d after CNS injury, whereas brevican and versican are not expressed in the chronic glial scar. Neurocan is also expressed by astrocytes in primary cell culture. Relative to the amount present in cultured astrocytes or uninjured cortex, neurocan expression increases significantly in the glial scar resulting from cortical injury, including the re-expression of the neonatal isoform of neurocan. In contrast, phosphacan protein levels are decreased in the glial scar compared with the uninjured brain. Because these CS-PGs are capable of inhibiting neurite outgrowth in vitro, our data suggest that phosphacan and neurocan in areas of reactive gliosis may contribute to axonal regenerative failure after CNS injury.

N(epsilon)-(carboxymethyl)lysine adducts of proteins are ligands for receptor for advanced glycation end products that activate cell signaling pathways and modulate gene expression

Recent studies suggested that interruption of the interaction of advanced glycation end products (AGEs), with the signal-transducing receptor receptor for AGE (RAGE), by administration of the soluble, extracellular ligand-binding domain of RAGE, reversed vascular hyperpermeability and suppressed accelerated atherosclerosis in diabetic rodents. Since the precise molecular target of soluble RAGE in those settings was not elucidated, we tested the hypothesis that predominant specific AGEs within the tissues in disorders such as diabetes and renal failure, N(epsilon)-(carboxymethyl)lysine (CML) adducts, are ligands of RAGE. We demonstrate here that physiologically relevant CML modifications of proteins engage cellular RAGE, thereby activating key cell signaling pathways such as NF-kappaB and modulating gene expression. Thus, CML-RAGE interaction triggers processes intimately linked to accelerated vascular and inflammatory complications that typify disorders in which inflammation is an established component.

cDNA cloning of a novel secreted isoform of the human receptor for advanced glycation end products and characterization of cells co-expressing cell-surface scavenger receptors and Swedish mutant amyloid precursor protein

The receptor for advanced glycation end products (RAGE) has been proposed as a cell surface receptor that binds amyloid-beta protein (Abeta), thereby triggering its cytotoxic effects [S.D. Yan, X. Chen, J. Fu, M. Chen, H. Zhu, A. Roher, T. Slattery, L. Zhao, M. Nagashima, J. Morser, A. Migheli, P. Nawroth, D. Stern, A.M. Schmidt, RAGE and amyloid-beta peptide neurotoxicity in Alzheimer's disease, Nature 382 (1996) 685-691.]. A cDNA library of human lung was screened for RAGE with an appropriate hybridization probe. In addition to cell surface RAGE, one clone was found which encodes a new version of RAGE, termed hRAGEsec, which lacks the 19 amino acids of the membrane-spanning region and is therefore secreted. Comparison with the genomic sequence revealed that the synthesis of the secreted isoform requires alternative splicing. The deduced protein sequence of the mature hRAGEsec consists of 321 amino acids with a predicted molecular mass of 35.66 kDa. The pattern of expression of hRAGEsec in human brain was analyzed by in situ hybridization histochemistry. The most intense expression of the gene in contrast to cell surface RAGE was detected in hippocampal CA3 pyramidal cells, dentate gyrus granule cells, cortical neurons as well as glial cells in white matter. To investigate the interaction between Abeta and RAGE and another scavenger receptor, SRA, under physiological conditions, they were co-expressed with human betaAPP(695)-SFAD in a human cell and the level of Abeta in the condition medium was assessed by immunoprecipitation and enzyme-linked immunosorbent assay (ELISA) analysis. A nearly 100% reduction of Abeta from the conditioned medium of hRAGE cells and approximately 40% reduction from the SRA-cells implied that hRAGE could be a prominent cell surface receptor interacting with Abeta.

Receptor for advanced glycation end products (RAGE)-mediated neurite outgrowth and activation of NF-kappaB require the cytoplasmic domain of the receptor but different downstream signaling pathways

Receptor for advanced glycation end products (RAGE) mediates neurite outgrowth in vitro on amphoterin-coated substrates. Ligation of RAGE by two other ligands, advanced glycation end products or amyloid beta-peptide, is suggested to play a role in cell injury mechanisms involving cellular oxidant stress and activation of the transcription factor NF-kappaB. However, the RAGE signaling pathways in neurite outgrowth and cell injury are largely unknown. Here we show that transfection of RAGE to neuroblastoma cells induces extension of filopodia and neurites on amphoterin-coated substrates. Furthermore, ligation of RAGE in transfected cells enhances NF-kappaB-dependent transcription. Both the RAGE-mediated neurite outgrowth and activation of NF-kappaB are blocked by deletion of the cytoplasmic domain of RAGE. Moreover, dominant negative Rac and Cdc42 but not dominant negative Ras inhibit the extension of neurites induced by RAGE-amphoterin interaction. In contrast, the activation of NF-kappaB is inhibited by dominant negative Ras but not Rac or Cdc42. These data suggest that distinct signaling pathways are used by RAGE to induce neurite outgrowth and regulate gene expression through NF-kappaB.

HMG-1 as a late mediator of endotoxin lethality in mice

Endotoxin, a constituent of Gram-negative bacteria, stimulates macrophages to release large quantities of tumor necrosis factor (TNF) and interleukin-1 (IL-1), which can precipitate tissue injury and lethal shock (endotoxemia). Antagonists of TNF and IL-1 have shown limited efficacy in clinical trials, possibly because these cytokines are early mediators in pathogenesis. Here a potential late mediator of lethality is identified and characterized in a mouse model. High mobility group-1 (HMG-1) protein was found to be released by cultured macrophages more than 8 hours after stimulation with endotoxin, TNF, or IL-1. Mice showed increased serum levels of HMG-1 from 8 to 32 hours after endotoxin exposure. Delayed administration of antibodies to HMG-1 attenuated endotoxin lethality in mice, and administration of HMG-1 itself was lethal. Septic patients who succumbed to infection had increased serum HMG-1 levels, suggesting that this protein warrants investigation as a therapeutic target.

RAGE mediates a novel proinflammatory axis: a central cell surface receptor for S100/calgranulin polypeptides

S100/calgranulin polypeptides are present at sites of inflammation, likely released by inflammatory cells targeted to such loci by a range of environmental cues. We report here that receptor for AGE (RAGE) is a central cell surface receptor for EN-RAGE (extracellular newly identified RAGE-binding protein) and related members of the S100/calgranulin superfamily. Interaction of EN-RAGEs with cellular RAGE on endothelium, mononuclear phagocytes, and lymphocytes triggers cellular activation, with generation of key proinflammatory mediators. Blockade of EN-RAGE/RAGE quenches delayed-type hypersensitivity and inflammatory colitis in murine models by arresting activation of central signaling pathways and expression of inflammatory gene mediators. These data highlight a novel paradigm in inflammation and identify roles for EN-RAGEs and RAGE in chronic cellular activation and tissue injury.

Characterization of the advanced glycation end-product receptor complex in human vascular endothelial cells

Advanced glycation end products (AGEs) have been implicated as causal factors in the vascular complications of diabetes and it is known that these products interact with cells through specific receptors. The AGE-receptor complex, originally described as p60 and p90, has been characterised in hemopoietic cells and the component proteins identified and designated AGE-R1, -R2 and -R3. In the current study we have characterised this receptor in human umbilical vein endothelial cells (HUVECs) and elucidated several important biological properties which may impact on AGE mediated vascular disease. 125I-AGE-BSA binding to HUVEC monolayers was determined with and without various cold competitors. The synthetic AGE, 2-(2-furoyl)-4(5)-furanyl-1H-imidazole (FFI)-BSA, failed to compete with AGE-BSA binding unlike observations already reported in hemopoietic cells. The ability of 125I-AGE-BSA to bind to separated HUVEC plasma membrane (PM) proteins was also examined and the binding at specific bands inhibited by antibodies to each component of the AGE-receptor complex. Western blotting of whole cell and PM fractions, before and after exposure to AGE-BSA, revealed that AGE-R1, -R2 and -R3 are subject to upregulation upon exposure to their ligand, a phenomenon which was also demonstrated by immunofluorescence of non-permeabilised cells. mRNA expression of each AGE-receptor component was apparent in HUVECs, with the AGE-R2 and -R3 gene expression being upregulated upon exposure to AGEs in a time-dependent manner. A phosporylation assay in combination with AGE-R2 immunoprecipitation demonstrated that this component of the receptor complex is phosphorylated by acute exposure to AGE-BSA. These results indicate the presence of a conserved AGE-receptor complex in vascular endothelium which demonstrates subtle differences to other cell-types. In response to AGE-modified molecules, this complex is subject to upregulation, while the AGE-R2 component also displays increased phosphorylation possibly leading to enhanced signal transduction.

Activation of receptor for advanced glycation end products: a mechanism for chronic vascular dysfunction in diabetic vasculopathy and atherosclerosis

Receptor for advanced glycation end products (RAGE) is a member of the immunoglobulin superfamily of cell surface molecules and engages diverse ligands relevant to distinct pathological processes. One class of RAGE ligands includes glycoxidation products, termed advanced glycation end products, which occur in diabetes, at sites of oxidant stress in tissues, and in renal failure and amyloidoses. RAGE also functions as a signal transduction receptor for amyloid beta peptide, known to accumulate in Alzheimer disease in both affected brain parenchyma and cerebral vasculature. Interaction of RAGE with these ligands enhances receptor expression and initiates a positive feedback loop whereby receptor occupancy triggers increased RAGE expression, thereby perpetuating another wave of cellular activation. Sustained expression of RAGE by critical target cells, including endothelium, smooth muscle cells, mononuclear phagocytes, and neurons, in proximity to these ligands, sets the stage for chronic cellular activation and tissue damage. In a model of accelerated atherosclerosis associated with diabetes in genetically manipulated mice, blockade of cell surface RAGE by infusion of a soluble, truncated form of the receptor completely suppressed enhanced formation of vascular lesions. Amelioration of atherosclerosis in these diabetic/atherosclerotic animals by soluble RAGE occurred in the absence of changes in plasma lipids or glycemia, emphasizing the contribution of a lipid- and glycemia-independent mechanism(s) to atherogenesis, which we postulate to be interaction of RAGE with its ligands. Future studies using mice in which RAGE expression has been genetically manipulated and with selective low molecular weight RAGE inhibitors will be required to definitively assign a critical role for RAGE activation in diabetic vasculopathy. However, sustained receptor expression in a microenvironment with a plethora of ligand makes possible prolonged receptor stimulation, suggesting that interaction of cellular RAGE with its ligands could be a factor contributing to a range of important chronic disorders.

Receptors for proteins modified by advanced glycation endproducts (AGE)--their functional role in atherosclerosis

Long-term incubation of proteins with glucose leads, through the formation of early stage products such as Schiff base and Amadori rearrangement products, to the formation of advanced glycation end products (AGE). Recent studies of AGE-structures as well as the receptor for AGE-proteins (AGE-receptors) have emphasized the involvement of protein modification by AGE in aging and age-enhanced disease processes. Immunohistochemical analyses of human atherosclerotic lesions using a monoclonal anti-AGE antibody have demonstrated diffuse extracellular AGE-deposition as well as dense intracellular AGE-deposition in macrophage- and vascular smooth muscle cell (SMC)-derived foam cells. In vitro experiments using both CHO cells overexpressing macrophage scavenger receptor-A (MSR-A) and peritoneal macrophages from MSR-A-knockout mice have shown that the MSR-A plays a major role in endocytic uptake of AGE-proteins by macrophages. Furthermore, in vitro experiments with rabbit arterial SMCs demonstrated a novel AGE-receptor mediating endocytosis of AGE-proteins. These in vivo and in vitro experiments suggest that AGE-proteins formed extracellularly in atherosclerotic lesions are endocytosed by macrophages through MSR-A in the early stage, and by SMCs through the novel AGE-receptor in the advanced stage, implicating functional contribution of the AGE-receptor-mediated interaction of AGE-proteins with these cells to atherosclerotic processes in arterial walls.

Decrease with age in methylcytosines in the promoter region of receptor for advanced glycated end products (RAGE) gene in autopsy human cortex

Changes with age in the methylation status of cytosines in the promoter region of the receptor for advanced glycated end products (RAGE) in autopsy human cortex were investigated, using the bisulfite method, polymerase chain reaction (PCR), and direct sequencing of PCR products. The total number of methylcytosines significantly decreased with age. While the number of methylated cytosines at CpG dinucleotides was stable throughout adult life, that at sites other than CpG dinucleotides significantly decreased with age in cases >/=70 years old. Of 13 transcription factor binding sites, cytosines in CpG doublets in NF-IL6 and SP-1 binding sites were methylated in all cases, suggesting that these sites are repressed throughout adulthood. In contrast, the number of methylcytosines in AP-2 or SP-1 binding sites located at CpC, CpA, or CTG was significantly lower or at least tended to be lower in cases >/=70 years than <70 years old. These reductions in the number of methylcytosines at transcription factor binding sites may increase expression of RAGE, which may in turn play a role in aging of the brain.

[Non-enzymatic glycation and oxidative stress in chronic illnesses and diabetes mellitus]

New approaches in biochemistry and molecular biology have increased the knowledge on the pathophysiology of chronic diseases as late diabetic complications, Alzheimer's disease, arteriosclerosis and vascular disease by defining the concept of "AGE-formation and oxidative stress." Nonenzymatic glycation, in which reducing sugars are covalently bound to free aminogroups of macromolecules, results in the formation of Advanced Glycation End products (AGEs) which accumulate during aging and at accelerated rate during the course of diabetes. Glycation accompanying oxidation processes support AGE-formation. AGE-formation changes the physicochemical properties of proteins, lipids and nucleic acids. In addition, binding of AGEs to specific surface receptors induces cellular signalling and cell activation. Interaction of AGEs with one of the receptors, RAGE, generates intracellular oxidative stress, which results in activation of the transcription factor NF-kappa B and subsequent gene expression, which might be relevant in late diabetic complications.

CONCLUSION

Knowledge of the basis molecular mechanisms allows to understand the interplay of different inducers such as redicals, cytokines, AGE-proteins and amyloid-beta-peptids and to define oxidative stress as a "common endpoint" of cell dysfunction. With respect to therapeutic options it is now possible not only to optimize blood glycemic control, but also to design drugs such as AGE-inhibitors and AGE-"cross-link" breakers. In addition patients with chronic disease associated with increased oxidative stress ay benefit from an antioxidant rich (and AGE protein poor?) nutrition.

Simple and fast method to test the receptor for advanced glycosylated endproducts (RAGE) for its tumor suppressive potential using the Tet-On system

The Tet gene expression system, that allows tightly controlled gene expression in response to doxycycline, was applied to analyze the influence of the receptor for advanced glycosylation endproducts (RAGE) on the growth of 293 cells in semi-solid medium. Establishing a Tet-On gene expression system involves two consecutive stable transfections. Here, we describe an alternative procedure to obtain a Tet-On gene expression system in a single transfection step for the use in tumor biology. The plasmids necessary for the regulated expression of RAGE together with the selectable marker plasmid were cotransfected in a molar ratio of 6:1. After aminoglycoside selection, 29 clones were analyzed using PCR revealing 8 colonies to be double stably transformed. Subsequent Western blot analysis showed inducible expression in 7 cell lines. Applying the one step protocol, the entire Tet-On expression system could be completed in half of the time required for the original two step method. The generated 293 double stable cells were used in the clonogenic assay for the testing of the tumor suppressive potential of RAGE.

Sp1-binding elements in the promoter of RAGE are essential for amphoterin-mediated gene expression in cultured neuroblastoma cells

Receptor for AGE (RAGE) and the polypeptide amphoterin are highly expressed and co-localized in neurons of the developing central nervous system of the rat. In vitro, the interaction of amphoterin with neuronal RAGE induces neurite outgrowth. We tested the hypothesis that interaction of amphoterin with neuronal cells enhances RAGE expression, thereby providing a mechanism by which amphoterin-mediated regulation of RAGE might contribute to promotion of neurite growth and spreading. Incubation of cultured neuroblastoma cells with amphoterin resulted in increased transcription and translation of RAGE, a process largely inhibited in the presence of anti-RAGE IgG but not by nonimmune IgG. To begin to delineate molecular mechanisms underlying these findings, we identified multiple putative binding elements within the 5'-flanking region of the RAGE gene for Sp1, a transcription factor that has been critically linked to the process of normal development. DNase I footprinting and electrophoretic mobility shift assays demonstrated multiple functional Sp1-binding sites within the region -245 to -40 of the RAGE promoter. Transient transfection of cultured SK-N-SH neuroblastoma cells with chimeric 5'-deletion constructs linked to luciferase reporter revealed that the region containing Sp1-binding elements did not contribute uniquely to basal expression of the RAGE gene. Simultaneous mutation of the multiple Sp1-binding elements in this region did not affect basal promoter function; however, promoter responsiveness to amphoterin was markedly attenuated. These results point to Sp1-dependent mechanisms underlying amphoterin-mediated increases in RAGE expression in neuroblastoma cells and further link amphoterin-RAGE interaction to development of the nervous system.

Diabetes, advanced glycation endproducts and vascular disease

The high incidence of vascular complications in patients with diabetes mellitus remains incompletely understood. Several metabolic or endocrine abnormalities have been postulated as possible triggers for micro and macroangiopathies. This review article focuses on the consequences of hyperglycemia, leading to the formation of advanced glycation endproducts (AGE), on vascular function. Advanced glycation endproducts are the product of the binding of aldoses onto free amino groups of proteins or lipoproteins, which, after molecular rearrangement, result in a class of molecules of a brown color and specific fluorescence. Different cell membrane proteins have been shown to bind AGE and the best characterized receptor for AGE has been named RAGE. The AGE receptor is present on different cell types including endothelial cells, smooth muscle cells, lymphocytes and monocytes. Experimental studies have revealed that the binding of AGE to RAGE produces an activation of monocytes and endothelial cells. Activated endothelial cells produce interleukin and express vascular cell adhesion molecule and tissue factor. Advanced glycation endproducts, when infused into animals, induce an increase in vascular permeability. The blockade of RAGE by specific antibodies corrects the hypermeability observed in diabetic animals. The prevention of AGE formation by aminoguanidine treatment improves the microvascular lesions found in diabetic animals either in the retina or the glomerus. The infusion of recombinant RAGE in diabetic animals corrects hyperpermeability. The colocalization of RAGE and AGE at the microvascular site of the injury suggests that their interaction may play a significant role in the pathogenesis of diabetic vascular lesions.

A murine model of accelerated periodontal disease in diabetes

Diabetes is a risk factor for periodontal disease in humans. In hyperglycemia, glycoxidation of proteins and lipids results in the formation of advanced glycation endproducts, or AGEs. The accumulation of AGEs in the plasma and tissues, and their interaction with their cellular receptor for AGE (RAGE), has been implicated in diabetic complications. In order to establish a model with which to delineate the specific host response factors that underlie the development of periodontal disease in diabetes, male C57BL/6J mice were rendered diabetic with streptozotocin. One month after documentation of diabetes or control state, mice were inoculated with the human periodontal pathogen Porphyromonas gingivalis, strain 381 (P. gingivalis) or treated with vehicle. Infection with P. gingivalis was achieved, as demonstrated by infiltration of gingival tissue with granulocytes, presence of DNA specific for P. gingivalis as well as increased serum antibody titer to P. gingivalis. At 2 and 3 months after infection, increased alveolar bone loss was demonstrated in P. gingivalis-inoculated diabetic vs. non-diabetic mice, along with enhanced tissue-destructive capacity, as demonstrated by increased collagenolytic activity in gingival extracts. Consistent with an important role for AGE-RAGE interaction, increased AGE deposition and expression of vascular and monocyte RAGE were demonstrated in diabetic gingiva compared with non-diabetic controls. Taken together, these data indicate that we have established a murine model of enhanced periodontal disease in diabetes. This model will serve to delineate molecular mechanisms which account for the increased susceptibility of diabetic patients to periodontal disease.

An endothelial growth factor involved in rat renal development

In the kidney, there is a close and intricate association between epithelial and endothelial cells, suggesting that a complex reciprocal interaction may exist between these two cell types during renal ontogeny. Thus, we examined whether metanephrogenic mesenchymal cells secrete endothelial mitogens. With an endothelial mitogenic assay and sequential chromatography of the proteins in the media conditioned by a cell line of rat metanephrogenic mesenchymal cells (7.1.1 cells), we isolated a protein whose amino acid analysis identified it as hepatoma-derived growth factor (HDGF). Media conditioned with Cos-7 cell transfected with HDGF cDNA stimulated endothelial DNA synthesis. With immunoaffinity purified antipeptide antibodies, we found that HDGF was widely distributed in the renal anlage at early stages of development but soon concentrated at sites of active morphogenesis and, except for some renal tubules, disappeared from the adult kidney. From a 7.1.1 cells cDNA library, a clone of most of the translatable region of HDGF was obtained and used to synthesize digoxigenin-labeled riboprobes. In situ hybridization showed that during kidney development mRNA for HDGF was most abundant at sites of nephron morphogenesis and in ureteric bud cells while in the adult kidney transcripts disappeared except for a small population of distal tubules. Thus, HDGF is an endothelial mitogen that is present in embryonic kidney, and its expression is synchronous with nephrogenesis.

Expression of HNK-1 carbohydrate and its binding protein, SBP-1, in apposing cell surfaces in cerebral cortex and cerebellum

Sulfoglucuronyl carbohydrate is the terminal moiety of neolacto-oligosaccharides, expressed on several glycoproteins of the immunoglobulin superfamily involved in cell-cell recognition and on two glycolipids. Sulfoglucuronyl carbohydrate is temporally and spatially regulated in the developing nervous system. It appears to be involved in neural cell recognition and in cell adhesion processes through its interaction with specific proteins on cell surfaces. Previously we have characterized a specific sulfoglucuronyl carbohydrate-binding protein in rat brain. Sulfoglucuronyl carbohydrate binding protein-1 is structurally similar to a 30,000 mol. wt adhesive and neurite outgrowth promoting protein amphoterin [Rauvala and Pihlaskari (1987) J. biol. Chem. 262, p. 16,625]. The pattern of expression of sulfoglucuronyl carbohydrate binding protein-1 in developing rat nervous system was studied to understand the significance of its interaction with sulfoglucuronyl carbohydrate-bearing molecules. Biochemical analyses showed that the expression of sulfoglucuronyl carbohydrate binding protein-1 was developmentally regulated similarly to sulfoglucuronyl carbohydrate. Immunocytochemical localization of sulfoglucuronyl carbohydrate binding protein-1 and sulfoglucuronyl carbohydrate was performed by bright-field and fluorescent confocal laser scanning microscopy. In postnatal day 7 rat cerebellum, sulfoglucuronyl carbohydrate binding protein-1 was primarily associated with neurons of the external and internal granule cell layers. The sulfoglucuronyl carbohydrate binding protein-1 immunoreactivity was absent in Purkinje cell bodies and their dendrites in the molecular layer, as well as in Bergmann glial fibres and in white matter. In contrast, sulfoglucuronyl carbohydrate (reactive with HNK-1 antibody) was localized in processes surrounding granule neurons in the internal granule cell layer. Sulfoglucuronyl carbohydrate was also expressed in Purkinje neurons and their dendrites in the molecular layer and their axonal processes in the white matter. To a lesser extent Bergmann glial fibres were also positive for sulfoglucuronyl carbohydrate. In the cerebral cortex, at embryonic day 21, sulfoglucuronyl carbohydrate binding protein-1 was mainly observed in immature neurons of the cortical plate and subplate and dividing cells near the ventricular zone. Whereas, sulfoglucuronyl carbohydrate was strongly expressed in the fibres of the subplate and marginal zone. Sulfoglucuronyl carbohydrate was also found in the processes surrounding the sulfoglucuronyl carbohydrate binding protein-1-expressing neuronal cell bodies in the cortical plate and in ventricular zone. The specific localization of sulfoglucuronyl carbohydrate binding protein- in cerebellar granule neurons and neurons of the cerebral cortex was also confirmed by immunocytochemistry of the dissociated tissue cell cultures. The complementary localization of sulfoglucuronyl carbohydrate and sulfoglucuronyl carbohydrate binding protein-1, both in cerebral cortex and cerebellum, in apposing cellular structures indicate possible interaction between the two and signalling during the process of cell migration and arrest of migration.

faint sausage encodes a novel extracellular protein of the immunoglobulin superfamily required for cell migration and the establishment of normal axonal pathways in the Drosophila nervous system

We examined the structure of the nervous system in Drosophila embryos homozygous for a null mutation in the faint sausage (fas) gene. In the peripheral nervous system (PNS) of fas mutants, neurons fail to delaminate from the ectodermal epithelium; in the central nervous system (CNS), the positions of neuronal cell bodies and glial cells are abnormal and normal axonal pathways do not form. Sequence analysis of fas cDNAs revealed that the fas protein product has characteristics of an extracellular protein and that it is a novel member of the immunoglobulin (Ig) superfamily. In situ hybridization demonstrated that fas transcripts are expressed throughout the embryo but they are in relatively high concentrations in the lateral ectoderm, from which the peripheral nervous system delaminates and in the CNS. Antiserum directed against Fas protein was found to stain neurons but not glia in the CNS. We conclude that fas encodes a protein that, in the developing nervous system, is present on the surface of neurons and is essential for nerve cell migration and the establishment of axonal pathways.

Cortactin-Src kinase signaling pathway is involved in N-syndecan-dependent neurite outgrowth

N-syndecan (syndecan-3) was previously isolated as a cell surface receptor for heparin-binding growth-associated molecule (HB-GAM) and suggested to mediate the neurite growth-promoting signal from cell matrix-bound HB-GAM to the cytoskeleton of neurites. However, it is unclear whether N-syndecan would possess independent signaling capacity in neurite growth or in related cell differentiation phenomena. In the present study, we have transfected N18 neuroblastoma cells with a rat N-syndecan cDNA and show that N-syndecan transfection clearly enhances HB-GAM-dependent neurite growth and that the transfected N-syndecan distributes to the growth cones and the filopodia of the neurites. The N-syndecan-dependent neurite outgrowth is inhibited by the tyrosine kinase inhibitors herbimycin A and PP1. Biochemical studies show that a kinase activity, together with its substrate(s), binds specifically to the cytosolic moiety of N-syndecan immobilized to an affinity column. Western blotting reveals both c-Src and Fyn in the active fractions. In addition, cortactin, tubulin, and a 30-kDa protein are identified in the kinase-active fractions that bind to the cytosolic moiety of N-syndecan. Ligation of N-syndecan in the transfected cells by HB-GAM increases phosphorylation of c-Src and cortactin. We suggest that N-syndecan binds a protein complex containing Src family tyrosine kinases and their substrates and that N-syndecan acts as a neurite outgrowth receptor via the Src kinase-cortactin pathway.